189 UN member states as well as two observers, namely the Holy See and the State of Palestine, have become parties to the NPT. However, one of these states (North Korea) submitted a notice of withdrawal. See the section #Withdrawn state below for more details.

Multiple dates indicate the different days in which states submitted their signature or deposition, varied by location. This location is noted by: (L) for London, (M) for Moscow, and (W) for Washington D.C.

Bolded states with a dagger (†) are recognized as nuclear weapons states by the treaty.

The Republic of China (Taiwan), which is currently only recognized by 11 UN member states, ratified the treaty prior to the United Nations General Assembly's vote to transfer China's seat to the People's Republic of China (PRC) in 1971. When the PRC subsequently ratified the treaty, they described the Republic of China's (ROC) ratification as "illegal". The ROC has committed itself to continue to adhere to the requirements of the treaty, and the United States has declared that it still regards the authorities in Taiwan to be bound by the NPT's obligations.^[9][12]

Article X.1 allows a state to leave the treaty if "extraordinary events, related to the subject matter of this Treaty, have jeopardized the supreme interests of its country", giving three months notice. The state is required to give reasons for leaving the NPT in this notice, and to provide this notice to other NPT Parties and to the UN Security Council. This Article does not provide for other states to question a state's interpretation of "supreme interests of its country".

North Korea acceded to the NPT in 1985. On 12 March 1993, after it was found in non-compliance with its safeguards agreement, North Korea gave notice to withdraw from the NPT. However, on 11 June 1993, one day before the withdrawal was to take effect, North Korea reached agreement with the United States to freeze its nuclear program under the Agreed Framework and "suspended" its withdrawal notice.^[13] In October 2002, the United States accused North Korea of violating the Agreed Framework by pursuing a secret uranium enrichment program, and suspended shipments of heavy fuel oil under that agreement. In response, North Korea expelled IAEA inspectors, disabled IAEA equipment and, on 10 January 2003, announced that it was ending the suspension of its previous NPT withdrawal notification.^[1][2] There is disagreement among the parties to the treaty whether North Korea's withdrawal was in conformity with the terms of the treaty.^[14][2] North Korea said that only one more day's notice was sufficient for withdrawal from the NPT, as it had given 89 days before.^[15] The IAEA Board of Governors rejected this interpretation.^[16] Most countries held that a new three-months withdrawal notice was required, and some^[who?] questioned whether North Korea's notification met the "extraordinary events" and "supreme interests" requirements of the Treaty.^{[citation needed]} The Joint Statement of 19 September 2005 at the end of the Fourth Round of the Six-Party Talks called for North Korea to "return" to the NPT, implicitly acknowledging that it had withdrawn. As of October, 2016, North Korea has conducted five announced nuclear tests between October 9, 2006, to September 9, 2016.^[17]

In 2020, Iran threatened to withdraw from the NPT if it is referred to the United Nations Security Council for alleged breaching the Joint Comprehensive Plan of Action.^[18]

Four UN member states have never been a party to the treaty.

The Cook Islands and Niue, two associated states of New Zealand which have had their "full treaty-making capacity" recognised by United Nations Secretariat,^[5] are not parties to the treaty but consider themselves bound by its provisions by virtue of their administration by New Zealand when the latter ratified the NPT.^[6]

• List of parties to the Biological Weapons Convention
• List of parties to the Chemical Weapons Convention
• List of parties to the Convention on Certain Conventional Weapons
• List of parties to the Comprehensive Nuclear-Test-Ban Treaty
• List of parties to the Ottawa Treaty
• List of parties to the Partial Nuclear Test Ban Treaty
• List of parties to the Treaty on the Prohibition of Nuclear Weapons
• List of parties to weapons of mass destruction treaties